Method of producing cast refractories



Patented July 22, 1952 METHOD OF PRODUCING CAST REFRACTORIES Theodore E. Field, Louisville, Ky., and Harold T. Smyth, Takoma Park, Md., assignors to Corhart Refractories Company, Louisville, Ky.

No Drawing. Application March 5, 1948, Serial No. 13,350

7 Claims. 1

" Heat' cast refractories hitherto produced by complete fusion of oxide ores and casting the melt into molds of desired shapes have generally suffered' fromthe presence of a relatively large centralvoid or pipe produced by the decrease in volume on conversion of the liquid into a crystalline solid on'cooling. In U. S. Patent 2,381,945 we have disclosed a technique for distributing such void into a multiplicity of minute and harmless pores throughout the casting by adding appropriate gasifiers to the liquid being cast. Such gasifiers are added in the form of granular solids which under the influence of the high heat-of the molten refractory generate a gas by decomposition or volatilization. The requirement for successful pipe dispersion is that such gassing occur widely throughout the casting liquid and persist long enough to maintain closed pore porosity in that liquid last to freeze.

1 In the'patent referred to, a number of gasiiiers which would give a persistent action and produce numerous minute cells were disclosed. For mixing the gasifier with the liquid to insureactionthroughout the casting it was recommended that a weighed amount of the granular solid be slowly poured on the surface of the molten refractory stream throughout the castin'g' interval. It is the purpose of this invention to disclose new and improved techniques for distributing the gasifier into the casting liquid.

' The'useful gasifiers are in general lighter than "ing lip. This leads to relatively wide variations in the size of thepouring stream and consequently in the rate'of filling of a given size of mold.

Variations of 100% are not uncommon. This makes difficult the assurance that the ,gasifler is completely added and yet not too rapidly. If the casting fills before all the gasifier has been added, the deficiency will result in residual pipe. If addition. is made too rapidly it may exceed the capacity of the stream to accept and wet the gasifler. Since failure to achieve complete pipe dispersal in a certain'percentage of blocks is not apparent externally, this is a serious drawback of the technique.-

' Methods of improving the technique of adding the gasifier have since occurred to us however and form the basis of the present disclosure. It has been found that excellent pipe distribution can be obtained in relatively deep molds if the gasifier is placed in kraft paper envelopes attached to the interior face of the top of the mold and the mold is cast rapidly. In a rapid pour an inch of metal may form in the bottom of even a large mold within 5 seconds and apparently even kraft paper will hold the gasifier long enough for at least a thin layer of metal to cover the bottom of the mold before the gasifier is released. In the case of molds made from sand bonded with organic binders, the combustion of such binders almost immediately exhausts the oxygen of the air within the mold and thisv may be the secret of the delayed release of the gasifier. In support of this hypothesis it should be noted that such paper will burn extremely rapidly if subjected to radiation in an oxidizing atmosphere even at the distinctly lower maximum temperature obtainable with a platinum wound furnace. Even with the present reducing atmosphere it is presumed that the paper is charred beyond its ability to longer retain the gasifier within a few seconds at most and the latter then falls into the pool of liquid on the bottom of the mold while the inrush of additional liquid produces turbulence and mixing.

It is thought that the success of this technique aside from the quantitative addition of the gasifier to the liquidis that the delay permits an initial rapidly frozen layer of refractory to form on the mold surface'and insulate the remaining liquid which freezes at a more gradual rate and is less likely to entrap undispersed gasifler; The first skin of the refractory must freeze extremely rapidly for it is common for the surface to show wrinkles. Earlier attempts to add the gasifler by sifting it over the bottom surface of the mold before casting had to be abandoned because almost invariably some part of the gasifier would be enmeshed in the freezing skin and prevented from exerting its desired effect in the contained liquid.

.The paper envelopes containing the gasifler may be conveniently pasted in place with the same paste used in assembling sand molds. We prefer to use several smaller envelopes distributed over the mold top rather than a single large one in order that the mixing be aided by initial wide dispersion, particularly if the mold is much longer than it is wide. Furthermore, there is always the possibility in commercial work that an envelope is dislodged by accident or premature movement of the mold before the paste dries, in which case it falls to the bottom of the mold. It is an advantage of our new technique that such an occurrence is manifest in the casting itself which will show a bottom surface depression roughly corresponding to the envelope size, and the casting can be recognized and carefully examined and discarded if necessary. While such an accident with all the gasifier in one envelope would ob- 3 viouslylead; to. rejection of the, casting, the probability of rejection is greatly diminished if for example, the observed scar corresponds at most to loss of only one tenth the effectiveness of the amount of gasifier, and thisprobabilitycan 7.

be further reduced if desired by setting up the procedure to use excess gasifier on all molds.

While the above technique worked well onmost relatively deep molds there was still a percentage of failures on these and a verylarge percentage of failures on shallow molds, marked by multiple envelope scars on the bottom of the castings.

This was attributed at first to failure of the paste bond holding the envelopes in place but numeroustestswith stronger pastesfailed to improvema-tters. Finally when the hypothesis of the importance of delayed burning was evolved it"wa's suspected that envelope failure was occurringsomewhat earlier in the shallow molds and possibly the occasional failures in deep molds were caused by slow pouring. Experiments were accordingly carried out with the object of pro-- longing the period required for the container of the fgasifler to charto failure. This is a delicate adjustment because for the smaller (thinner) castings it is particularly important that the delavnot'be too great if subsequent mixing is to be sufficient. ,By using heavier material such as cardboard it is quite possible to fill the mold before the gasifier is released. On the hypothesis that the delay that is obtained is due to the deyelopment. of an oxygen poor atmosphere it was thoughtthatthebehavior of the paper envelope inl'the first. one or two seconds while the; reducatmosphere was being developed might be especially important. I

This led to trial of, various fireproofing techniques fortreatment of the paperenvelopes. Solutions of salts such as generally used for papers or textileahowever, were not sufficiently effective. It. wasfoundhowever that a. sodium silicate solutionipainted in a relatively thick layer over the exposed surface of the paper. envelopes apparently sealed. away the oxygen during the critical At any rate. comparison of molds with :treatedand untreated envelopes showed a decrease in bottom marking (by premature release) for'the'treated envelopes. which was tremendously significant statistically..

Our preferred technique therefore is. tov supply the mold with a. predetermined measured amount of granular gasifier distributed among several envelopes which are pasted. on the interior surface of the top slab of the mold and are further given a fireproofing treatment by applying,

at; least to the exposed side of the envelope, a .layerof sodium silicate.

entering stream of molten refractory. The type :of silicate used is apparently not critical, its

purpose" being to seal away oxygen for a. brief -moment. It has been found that a commercial 429Baum; solution with soda to silica ratio, of

:LOO to 3.25' is quite, satisfactory. What we claim is:

11- The improvement in the process of distributing. pipe'in. heat cast refractories by addition of granulated 'gasifiers to the liquid being cast which comprizes casting the molten refractory into a mold provided with at least one combustible container of the gasifier attached to an interior surface of the mold-distant the bottom, said container having been given a fireproofing treatment.

2. The improvement in the process of distributing pipe in heat cast refractories by addition of granulated gasifiers to the liquid being cast,

which comprizes casting molten refractory into a mold provided with at least one paper container of the gasifier attached to an interior surface of the mold distant from the bottom, said container having been given a fireprooflng treatment.

3, The improvement in the process of distributing pipe in heat cast refractories by addition of granulated gasifiers. to the liquid being cast, which comprizes casting moltenv refractory into a mold provided with. at) least one combustible container of the. gasifier. attached to aninterior surface" of the mold distantfrom the bottom. said container having been given a fireproofing'treatment with soluble silicate.

4. The improvement in the process of distributing pipe in heat castv refractories by addition of granulated gasifiers to the liquid being cast, which comprizes casting molten refractory into a mold provided with at least one paper container of the gasifier attached to an interior surface of the mold distant from the bottom, said container having been given a fireproofing treatment with soluble silicate.

5. The improvement in theprocess of distributing pipe in heat cast refractories by addition of granulated gasiflers to the liquid being cast. which comprizes attaching to the interior surface of the top of the mold at least one paper container of the gasifier, said container, having been. fireproofed with sodiumsilicate, andcasting molten refractory into the mold.

6.. The improvement in; the; process of distributing pipe in heat cast refractories by addition of granulated gasifiers to theliquid being cast, which comprises casting the molten refractory into amold provided with at least one combustible container of the gasifier; attached to an interior surface of the mold distant from the bottom, said container being disintegrable prior to contact with the rising liquid, and introducing the molten refractory into the mold at a rate to cover the bottom of the mold prior-to disintegration of the container.

7. The improvement in the process of distributing pipe in heat cast refractories by addition of granulated gasifiers to the liquid being cast, whichv comprises casting the molten refractory into a mold provided with at least one paper. container of the gasifier attached to an interior surface of the mold distant from the bottom, said container being disintegrable prior to contact with the rising liquid, and introducing the molten refractory into the mold at a rate to cover the bottom of the mold prior to disintegration of the container.

THEODORE E. FIELD. HAROLD T. SMYTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 786,009 Cowden Mar. 28, 1905 1,975,084 Davies Oct. 2, 1934 2,148,583 Rowe Feb. 28, 1939 2,381,945 Field et al Aug. 14, 1945 

1. THE IMPROVEMENT IN THE PROCESS OF DISTRIBUTING PIPE IN HEAT CAST REFRACTORIES BY ADDITION OF GRANULATED GASIFIERS TO THE LIQUID BEING CAST WHICH COMPRIZES CASTING THE MOLTEN REFACTORY INTO A MOLD PROVIDED WITH AT LEAST ONE COMBUSTIBLE CONTAINER OF THE GASIFIER ATTACHED TO AN INTERIOR SURFACE OF THE MOLD DISTANT FROM THE BOTTOM, SAID CONTAINER HAVING BEEN GIVEN A FIREPROOFING TREATMENT. 